ABSTRACT Genetic instability of the mitochondrial genome (mtDNA) plays an important role in human aging and disease. For example, mtDNA instability causes blindness, deafness, myopathy and severe encephalomyopathy in children, and contributes to muscle wasting, cancer progression, and neurodegeneration in aging adults. To this day though, no child has ever been cured or successfully treated for an inherited mtDNA disease, nor does a treatment exist for the mtDNA component of age-related diseases. To successfully design a therapeutic strategy, it will be important to identify molecular mechanisms that can either increase or decrease the pathology that is caused by mtDNA instability. We may then manipulate these pathways with drugs to prevent or delay these diseases. Identifying these pathways requires a flexible animal model that is well suited for ?discovery experiments?; therefore, we created a new animal model of mtDNA instability in the nematode C. elegans. Using CRISPR/Cas9 technology, we created an error prone allele of DNA polymerase gamma (polg- 1D207A), the enzyme that replicates the mitochondrial genome. Worms that carry this allele display an elevated rate of mtDNA mutation and depletion, two types of genetic instability that cause mtDNA disease in humans. Because of this genetic instability, polg-1D207A worms suffer from an age-related decline in mitochondrial respiration and muscle function, mimicking the pathology seen in human patients. We propose to screen these worms by RNAi to identify genes that can either increase or decrease the severity of mtDNA disease. With this strategy, we have already discovered that IGF-1/insulin signaling, mitochondrial protein quality control, mitochondrial dynamics, mTor signaling, autophagy and apoptosis, all control the severity of mtDNA disease in worms. The strongest modulator of mtDNA disease that we identified thus far, is the IGF-1/insulin signaling pathway. It has long been known that reduced IGF-1/insulin signaling has beneficial effects for the overall health of organisms; however, we have now identified a discrete set of diseases for which reduced IIS activity may have a direct therapeutic application. Since this pathway is well-understood, and numerous drugs and genetic mutants are available for experimentation, we are in a unique position to rapidly transform these initial observations into a comprehensive program that has immediate translational relevance. To initiate this program, we propose to dissect the molecular mechanisms by which reduced IGF-1/insulin signaling rescues worms from mtDNA disease. These experiments will provide deep insight into the etiology of mtDNA disease and demonstrate that the IIS pathway modulates mtDNA disease by numerous mechanisms, at multiple levels of organization. In addition, we will test the therapeutic potential of our findings by investigating whether reduced IIS activity can ameliorate mtDNA disease in mice as well. We anticipate that these experiments will demonstrate that reduced IGF-1/insulin signaling has broad beneficial effects for all forms mtDNA disease, and will thus be a powerful ally in our battle against mitochondrial disorders.